The present invention relates to a satellite communication system for broadcasting, in which information signals are transmitted to a plurality of receiving stations from transmitting stations through a communication satellite. More particularly, the invention relates to a satellite communication system for broadcasting, in which there is return of an answer signal, such as for confirming reception of an information signal or for requesting retransmission, after the information signals are transmitted to the receiving side.
A satellite communication system is generally effective for simultaneous distribution of a variety of data, such as news and stock market information, to every corner of the country because it has nationwide transmission coverage.
However, the satellite communication system must provide error correcting functions for the receiving signals. Namely, a receiving signal often includes errors caused by a large signal attenuation. This is often due to the receiving signal travelling a long distance between the communication satellite and the ground stations, and/or an increase of attenuation and noise due to rain fall, and other like environmental factors.
An error correcting function in satellite communication systems can be achieved either be a "Forward Error Correction" (FEC) system, in which redundancy bits are added to data to be transmitted and used for correction of a receipt signal, or by an "Automatic Repeat Request" (ARQ) system, in which an answer signal for confirming reception of an information signal from the receiving end is used. In general, either one or both of these corrective systems in combination are used in satellite communication systems.
Notwithstanding, it is difficult to perfectly correct errors of a receipt signal only with FEC, so that it is normally required to combine the FEC system with an ARQ system in order to avoid missing the receiving data. Therefore, it becomes necessary to generate and return an answer signal, such as a signal confirming receipt of the information signal and/or a signal requesting retransmission of the information signal to the transmitting side from the receiving side.
To return an answer signal to the transmission side via satellite, it is necessary to provide the receiving side of the satellite communication system with transmitters. As is known, transmitters for satellite communication are big and expensive so that it is a key factor to the cost of the overall satellite communication system. Accordingly, employing an ARQ system for a satellite communication system results in creating an expensive system.